It is known to use life safety devices within a building or other structure to detect various hazardous conditions and provide a warning to occupants of the building of the detected hazardous condition. Examples of well known life safety devices include smoke detectors and carbon monoxide detectors.
Due to the critical function of life safety devices, the devices are often battery powered, or are AC powered with one or more backup batteries, to prevent the devices from being disabled in the event of an AC power failure. As the level of the battery tends to decrease over time, life safety devices are typically provided with a battery voltage test circuit that periodically tests the battery level of the detector. When the battery voltage drops below a predetermined level at which it is determined that the battery should be replaced, a warning is triggered to advise the occupant of the building in which the device is installed that the battery needs replacement. The warning is usually an audible warning and/or a visual warning.
Despite the apparent safety value in providing a low battery warning, such warnings are sometimes a nuisance, particularly when the warning occurs at night while a person is trying to sleep. To eliminate the warning, some users resort to removing the battery. However, removing the battery is undesirable as it prevents operation of the life safety device so that the device no longer functions as intended.
For safety reasons, safety regulations do not permit the low battery warning to be permanently silenced. However, the use of life safety devices provided with the capability of temporarily silencing low battery warnings are known. Examples of devices that indicate a low battery and/or permit a user to temporarily silence a low battery warning includes U.S. Pat. Nos. 6,624,750, 6,081,197, 5,969,600, 5,686,885, 5,686,896, 4,287,517 and U.S. Patent Published Application Nos. 2003/0227387 and 2002/0130782.
For life safety devices that permit temporary silencing of a low battery warning, the low battery warning is silenced for a predetermined period of time. However, silencing the warning for a predetermined period of time presents various problems. For example, a user who silences the low battery warning knowing that it will be silenced for a predetermined period of time can procrastinate in replacing the battery for sake of convenience or to get the most life out of the battery. When the low battery warning sounds, the user may silence the warning and, knowing that the silence period will end after a predetermined time period, make it a point to return to silence the warning once again just prior to the end of the time period. The user may continue to do this for as long as possible, maximizing the use of the battery, until the battery level reaches a voltage threshold at which the user is no longer able to silence the warning.
Thus, there is a continuing need for improvements in life safety devices having silenceable low battery alarms.